Gases, such as natural gas, generally contain varying amounts of water vapor. It is desirable that no water vapor be admitted to a natural gas pipeline. The presence of the water vapor is undesirable as the water vapor can result in corrosion of pipes and cause corrosion of, and stoppages in, valves and fittings in gas pipe transmission systems. Further, quantities of water or moisture that are relatively small may freeze and block the pipeline such that flow is completely halted or at least greatly restricted.
A common method for removing moisture from gas streams, such as natural gas, is to use a gas dehydration unit using a glycol as a solvent. In such a unit, the wet gas is contacted with a lean drying agent solution, such as a glycol, in an absorbent step to remove the water. The glycol commonly used is triethylene glycol (TEG) and to a lesser extent other glycols such as diethylene glycol (DEG) or ethylene glycol (EG). The rich glycol (i.e., glycol containing the water) is then passed to a reconcentration or regeneration process typically comprising a reboiler wherein the absorbed water is driven off and removed, thereby enabling reuse of the regenerated glycol.
A troublesome problem arises herein, however, in that, simple heating of the drying agent may not remove a sufficient amount of water. The efficiency of the gas drying operation is a function of the residual water in the regenerated dehydrating agent. Raising the temperature during regeneration tends to drive off more moisture, but the use of excess heat also promotes degradation of the dehydrating agent by formation of pyrolysis products. These pyrolysis products in turn further reduce the effectiveness of the dehydrating agent.
Furthermore, such pyrolysis products may produce acids which may create corrosion problems in the gas dehydration units. To combat corrosion, drying agent compositions may comprise corrosion inhibitors, such as an alkanolamine. Commonly employed alkanolamines are, for example, monoethanolamine, diethanolamine, triethanolamine, etc. However, alkanolamines may be volatile and/or thermally unstable at dehydration reboiler temperatures.
Therefore, there still exists a need for a drying agent solution with improved thermal stability having corrosion inhibition properties.